Vinyl monomers (acrylic materials, etc.) and thermosetting resins (epoxy resins, phenolic resins, etc.) are conventionally used as adhesive materials.
However, volume shrinkage occurs during polymerization of such vinyl monomers and thermosetting resins, which leads to problems such as residual internal stress, cracking, and reduced adhesive strength.
The use of cyclic monomers as adhesive materials is being investigated with the aim of resolving the problems described above. Cyclic monomers are known to exhibit a smaller degree of polymerization shrinkage than vinyl monomers of equivalent molecular mass. Known examples of such cyclic monomers include vinylcyclopropanes, vinyloxiranes, 4-methylene-1,3-dioxolanes, cyclic ketene acetals, benzocyclobutenes, spiro orthocarbonates, spiro orthoesters, vinylcyclopropane cyclic acetals, cyclic allyl sulfides, and cyclic vinyl sulfones.
Among such cyclic monomers, vinylcyclopropanes are attracting particular attention. For example, a technique that involves using a polymer (homopolymer or copolymer) of a multifunctional vinylcyclopropane monomer (structural formula (1) shown below) as a dental material has been investigated (for example, refer to PTL 1). PTL 1 discloses that a copolymer of urethane dimethacrylate used as a vinyl monomer and a bis(vinylcyclopropane) used as a multifunctional vinylcyclopropane has improved mechanical properties and polymerization shrinkage compared to a copolymer of urethane dimethacrylate and dodecanediol dimethacrylate and a copolymer of urethane dimethacrylate and 1,1-bis(phenoxycarbonyl)-2-vinylcyclopropane.

However, materials based on vinyl monomers (acrylic materials, etc.) exhibit noticeably high polymerization shrinkage. Consequently, when the multifunctional vinylcyclopropane monomer described in PTL 1 is copolymerized with a material based on a vinyl monomer (acrylic material, etc.), there is a problem that polymerization shrinkage cannot be sufficiently suppressed, and it is thought that in such a situation, a monomer that exhibits as large a degree of volume expansion as possible is beneficial.
Compounds represented by structural formulae (2) to (4) shown below are also known multifunctional vinylcyclopropanes (for example, refer to NPL 1 and 2).
The compound represented by structural formula (2) shown below (volume change upon homopolymerization: −2.8%) and the compound represented by structural formula (4) shown below (volume change upon homopolymerization: −3.8%) have bulky substituents and exhibit a smaller degree of polymerization shrinkage than the compound represented by structural formula (3) shown below (volume change upon homopolymerization: −7.0%).
However, the fact that the compound represented by structural formula (2) shown below and the compound represented by structural formula (4) shown below do not exhibit volume expansion upon homopolymerization is a problem.
Up until the present time, a vinylcyclopropane that has a multifunctional structure and that also exhibits relatively large expansion has not been commonly known.



Furthermore, a monofunctional vinylcyclopropane that has adamantyl groups and that is represented by structural formula (5) shown below is a known example of a monofunctional vinylcyclopropane having bulky substituents that is a compound exhibiting excellent volume expansion (for example, refer to NPL 3).

However, the poor solubility of the compound represented by structural formula (5) in solvents such as acetone is problematic. Accordingly, a complicated process is required in production in order to obtain a polymer, which means that the aforementioned compound suffers from a problem of being disadvantageous in terms of convenience as a monomer.
Furthermore, a monofunctional vinylcyclopropane having an alicyclic compound introduced as a bulky substituent is known and variation of the number of ring members has been investigated (for example, refer to PTL 2 and 3).
Monomers described in PTL 2 and 3 suffer from a problem that despite polymerization shrinkage being mitigated, they do not exhibit volume expansion upon homopolymerization
As described above, a compound that exhibits volume expansion upon homopolymerization, maintains mechanical properties, and is highly convenient in production has yet to be developed and there is strong demand for development of such a compound.